Mac上python多线程错误：...+[__NSPlaceholderDate initialize]...

错误提示

objc[27880]: +[__NSPlaceholderDate initialize] may have been in progress in another thread when fork() was called.
objc[27880]: +[__NSPlaceholderDate initialize] may have been in progress in another thread when fork() was called. We cannot safely call it or ignore it in the fork() child process. Crashing instead. Set a breakpoint on objc_initializeAfterForkError to debug.

错误原因

刚开始以为是代码的问题，后来才发现其实是macOS的High Sierra以上的操作系统对多线程的限制。

解决办法

在环境变量中添加export OBJC_DISABLE_INITIALIZE_FORK_SAFETY=YES

• 终端

// 零时解决方法
// 在终端中执行以下命令，接着继续执行python程序
export OBJC_DISABLE_INITIALIZE_FORK_SAFETY=YES

// 永久解决方案
// 终端中执行以下命令
sudo echo "export OBJC_DISABLE_INITIALIZE_FORK_SAFETY=YES" >> ~/.bash_profile && source ~/.bash_profile

• PyCharm

// 在下面的选择中添加`OBJC_DISABLE_INITIALIZE_FORK_SAFETY=YES`，重启`PyCharm`即可
Run -> Edit Configuations... -> Environment variables